The present invention relates to machining of cylindrical parts. More specifically, the invention relates to a process and apparatus for machining long slender shafts.
Components for machines and mechanical apparatuses are typically machined to obtain precision tolerances and accurate surface conditions. Machining of the precision surfaces are typically machined by presenting a cutting tool or a grinding wheel against the precision surface.
During machining common precision parts include cylindrical parts. Cylindrical parts or workpieces are rotated about centers found at the ends thereof or supported on the periphery of the workpiece. Cylindrical parts which are relatively soft, having a hardness of Rockwell xe2x80x9cCxe2x80x9d scale (Rc) of 40 or less and which have medium tolerance requirements, for example xc2x10.002 inches in diameter tolerance, are typically turned on a turning machine with a cutting tool.
A lathe, for example, a numerically controlled lathe, is typically used to manufacture this type. of workpiece. The workpiece may be rotated about its centers by pressing in with centers on the lathe or, preferably, a portion of the outer periphery of the workpiece is clamped to provide sufficient torque required for the turning process.
More accurate or precision machining, i.e. for parts requiring a tolerance of less than +0.002 inches and/or for grinding materials having a hardness greater than, for example, 40 Rc is typically performed on a grinding machine utilizing a grinding wheel. Grinding of precision workpieces is accomplished by rotating the workpiece simultaneously with rotating a cylindrical grinding wheel in contact with the outer periphery of the workpiece. The workpiece is typically rotated about centers found at the end of the workpiece on a machine called a center-type grinder or may be supported on the periphery of the workpiece by a regulating wheel and a rest blade. Such peripheral support for a workpiece is performed on centerless-type grinders.
Long slender shafts requiring precision surfaces that may require a turning or a grinding to be performed thereon are used extensively in machines that pass a substrate through the machine. The long slender shafts are utilized to guide and direct the paper substrate through the machine and/or for performing operations on the substrate. For example, copying machines and printing machines have large substrates in the form typically of paper. The substrate may be in the form of a roll of paper or in the form of cut sheets.
Long shafts and, in particular, long, slender shafts such as those made from durable materials such as steel, deflect under the grinding or cutting of the workpiece. The deflection of the shafts affects the quality of the shafts and the precision requirements required for such shafts may be very difficult to obtain.
Attempts have been made to improve the quality of long thin shafts, which are turned or ground by reducing the deflection of the shaft during machining. The most common tool utilized in reducing the deflection of long thin workpieces is a work support or steady rest. The part deflection due to the force of the grinding wheel or cutting tool or simply due to the mass or weight of the workpiece is counteracted by the support from the steady rest. A further function of the steady rest is to prevent workpiece vibration and thereby to eliminate or reduce chatter.
An understanding of the use of steady rest is more thoroughly described in Modern Grinding Technology by Salmon, the relevant portions thereof incorporated herein by reference.
Referring now to FIG. 8, a prior art mechanically contacting steady rest is shown in FIG. 8. The standard steady rest is typically a 2 or 3 point contact tool that holds the part rigidly in place. For example, the steady rest 1 includes three fingers 2 which include contact points 3 which are equally spaced about roll 4. The fingers 3 are in contact with periphery 5 of the roll 4 and serve to support the roll 4 as it rotates about longitudinal axis 6. The work support 1 is secured to machine base 7.
In the well-known process of electrophotographic printing, a charge retentive surface, typically known as a photoreceptor, is electrostatically charged, and then exposed to a light pattern of an original image to selectively discharge the surface in accordance therewith. The resulting pattern of charged and discharged areas on the photoreceptor form an electrostatic charge pattern, known as a latent image, conforming to the original image. The latent image is developed by contacting it with a finely divided electrostatically attractable powder known as xe2x80x9ctoner.xe2x80x9d Toner is held on the image areas by the electrostatic charge on the photoreceptor surface.
Thus, a toner image is produced in conformity with a light image of the original being reproduced. The toner image may then be transferred to a substrate or support member (e.g., paper), and the image affixed thereto to form a permanent record of the image to be reproduced. Subsequent to development, excess toner left on the charge retentive surface is cleaned from the surface. The process is useful for light lens copying from an original or printing electronically generated or stored originals such as with a raster output scanner (ROS), where a charged surface may be imagewise discharged in a variety of ways.
While shafts in electrophotographic printing for guiding substrates require accurate tolerances and may be long and slender, exasperating the accurate tolerance problems, the difficulties encountered in providing accurate donor rolls for scavengeless development systems is particularly acute.
In a scavengeless development system, toner is detached from the donor roll by applying AC electric field to self-spaced electrode structures, commonly in the form of wires positioned in the nip between a donor roll and photoreceptor in the case of hybrid scavengeless development or by applying the AC electrical field directly to the donor roll in the case of hybrid jumping development. This forms a toner powder cloud in the nip and the latent image attracts toner from the powder cloud thereto. Because there is no physical contact between the development apparatus and the photoreceptor, scavengeless development is useful for devices in which different types of toner are supplied onto the same photoreceptor such as in xe2x80x9ctri-levelxe2x80x9d; xe2x80x9crecharge, expose and developxe2x80x9d; xe2x80x9chighlightxe2x80x9d; or xe2x80x9cimage on imagexe2x80x9d color xerography.
Since hybrid scavengeless development relies on a continuous, steady toner powder cloud at the nip between the latent image and the donor roller, the speeds at which the rollers operate are significantly higher and the accuracy requirements are much more precise.
The purpose and function of scavengeless development are described more fully in, for example, U.S. Pat. No. 4,868,600 to Hays et al., U.S. Pat. No. 4,984,019 to Folkins, U.S. Pat. No. 5,010,367 to Hays, or U.S. Pat. 5,063,875 to Folkins et al. U.S. Pat. No. 4,868,600 is incorporated herein by reference.
For proper operation of a donor roll in a hybrid scavengeless development, the diameter tolerance, runout and surface finish requirements of the donor roll are very critical and require very precise dimensions. Furthermore, donor rolls typically have a long length and a small diameter. For example, donor rolls may have a length of, for example, 18 to 24 inches and a diameter from 1 to 1xc2xd inches. When machining donor rolls with such a length to diameter ratio of 20 to 1 or greater, the rolls tend to deflect during the machining process. To complicate the situation, donor rolls may be made of a hard ceramic material which is difficult to machine. Because of the high tolerances and hard material, the donor rolls are often ground rather than turned. The grinding forces are typically higher than turning forces, thus causing the deflection during machining to increase.
Attempts have been made to reduce the deflection of rolls during the machining process. For example, mechanical supports are fixedly positioned underneath the roll during the machining process. These types of supports come in two particular designs. The support may be in the form of a steady rest which is fixedly positioned with respect to the roll and in the form of a follower rest which is mounted to the machining tool slide and moves with the material removal tool.
Mechanically contacting steady rests and follower rests have several problems. Mechanical steady rests consist of three equally spaced contact points against the roll as it is machined. Since the contact points typically in the form of pads or rollers are fixedly set, the contact points must be set to, for example, the unmachined dimensions and during the machining the contact points separate from the now-machined dimensions permitting the roll to deflect slightly under the machining forces.
The mechanically contacting steady rests and follower rests must be readjusted for each particular roll size that is to be machined on the machine. The contact points must be adjusted to contact the workpiece so that any change in the part diameter of a workpiece requires a changeover to the mechanical work support or steady rest setup. Furthermore, the setups are very difficult because selecting the optimum work. support setting related a work piece which part size is changing during the machining process is a trial and error process.
Furthermore, the mechanical contact work support tends to be bulky and may interfere with the position in which in process gauge fingers should otherwise be placed.
Also, when utilizing a mechanical follower rest, the installation of gauge fingers at the follower rest is very difficult.
Addition problems occur when machining ceramic materials utilizing a mechanical work support. The ceramic material is hard and very abrasive. When a material that is very hard is utilized at the contact points of the work support, the work support tends to burnish or wear the outer surface of the ceramic roll. When used for donor rolls, the electrical properties of the outer surface of the ceramic roll are adversely affected by a burnishing process, particularly if foreign material from the work rest is embedded into the roll. Furthermore, the burnishing may affect the size and the finish of the ceramic material.
When, alternatively, a soft material is utilized to support the ceramic roll, the support tends to wear excessively and loses its effectiveness by no longer totally supporting the roll. Furthermore, if a soft material is used for the work support, the outer surface of the work support becomes embedded into the ceramic material, further deteriorating the electrical properties of the ceramic roll.
Furthermore, the use of a mechanical steady rest makes adjustments for the proper fitting of the steady rest particularly during the machining process very difficult.
When utilizing a steady rest, the setup of the steady rest is very difficult in that not only the fit of the steady rest to the workpiece needs to be adjusted, but also the position of the mechanical steady rest needs to be adjusted. A series of steady rests may in fact be required to adequately support the part. Furthermore, the steady rest only serves to reduce chatter when the tool is positioned opposed to the support.
The following disclosures may be relevant to various aspects of the present invention:
The relevant portions of the foregoing disclosures may be briefly summarized as follows:
U.S. Pat. No. 5,527,210 discloses a dynamic steady rest particularly adapted for use in supporting a rotating workpiece during a grinding operation. The steady rest includes a lever assembly pivotally mounted on a base and having a workpiece support arm and a counterweight arm. Weights are adjustably secured to the counterweight arm and bias the support arm upwardly and into supporting engagement with the rotating workpiece. The steady rest further includes two dashpots pivotally secured between the base and the support arm to dampen the motion of the support arm.
U.S. Pat. No. 5,285,599 discloses a centering and supporting apparatus is disclosed for use as a true centering steady rest for rotatably supporting a cylindrical workpiece during a machining or grinding operation. The apparatus has an internal centerline adjustment mechanism for adjusting the steady rest so as to support the workpiece at its dynamic working centerline. At least one, or a pair of support arms are slidably mounted on an operator body in a housing. The one or pair of support arms each carries a side workpiece contact member, and the operator body carries a center workpiece contact member, and each workpiece contact member is engagable with the perimeter of the workpiece. The operator body is moved by a stroking means to urge the center workpiece to support a workpiece. The support arms are urged to support the workpiece by the action of cam followers carried by the support arms, and which cam followers are each engaged with a camming contour disposed in a guide plate that is displaceable within the housing by the internal centerline adjustment mechanism. The internal centerline adjustment mechanism allows either one or a pair of guide plates to be shifted within the steady rest to accommodate any deviation which the dynamic working centerline imposes from the static centerline originally established prior to a machining or grinding operation.
U.S. Pat. No. 4,831,782 discloses an improved grinding apparatus includes a base upon which a headstock is mounted. A carriage is movable along ways disposed on the base. A wheel slide on the carriage rotatably supports a grinding wheel. A first mounting plate extends beneath a first footstock and a first set of steady rests to a location adjacent to a headstock. While a workpiece is being ground, a second set of steady rests and a second footstock are mounted on a second mounting plate. When the grinding operation has been completed, the first mounting plate is disconnected from the base and removed from the grinding apparatus with the first set of steady rests and footstock. The second mounting plate with the second set of steady rests and footstock accurately positioned thereon are then inserted into the grinding apparatus.
U.S. Pat. No. 4,715,149 discloses a flow valve seat grinding apparatus incorporating an improved steady rest means. Includes a tubular drive shaft housing which houses and supports a rotatable and longitudinally movable drive shaft means. Drive shaft is connected through a flexible torque coupler to drive a valve seat grinding head. Grinding head is adapted to grind a valve seat located within a valve body. Includes adjustable anchor operable to laterally extend at least three anchor members into fixed anchoring contact with a sidewall of a valve body to laterally support the shaft housing in fixed position within the valve body.
U.S. Pat. No. 4,712,332 discloses a centerless grinding system comprises a driven grinding wheel, a driven regulating wheel, and a work rest blade for centerless grinding of a workpiece supported by the work rest blade between the grinding wheel and the regulating wheel; means for determining the rate of reduction of the workpiece radius while it is being ground; and means responsive to the rate of reduction of the workpiece radius for controlling the ratio of the power consumed in removing workpiece material to the rate of removal of workpiece material by the grinding wheel. The regulating wheel is preferably fed toward the grinding wheel to feed the workpiece into the grinding wheel. In a similar center-type grinding system, the workpiece is mounted on spindles or chucks which are movable toward the grinding wheel so that the workpiece can still be fed by the regulating wheel. Workpieces longer than the axial dimension of the grinding wheel are ground in successive plunges along the length of the workpiece, with the depth being controlled in each successive plunge. To grind hollow workpieces, the regulating wheel or grinding wheel is placed inside the hollow workpiece.
U.S. Pat. No. 4,711,054 discloses in a numerical control grinding machine using a grinding wheel made of cubic boron nitride, a computerized numerical controller controls the infeed movement of a wheel head to effect a rough grinding and a first fine grinding on a rotating cylindrical workpiece by the grinding wheel and to halt the first fine grinding in response to a sizing signal from a sizing device which measures the diameter of the workpiece being ground. At the halt of the first fine grinding, the numerical controller advances rest jaws to press the workpiece upon the grinding wheel until another sizing signal is issued from the sizing device. Until the number of the workpieces ground after each truing operation reaches a predetermined number, the numerical controller increase the infeed rate of the grinding wheel in each of the rough and first fine grindings toward a desired infeed rate on a step-by-step basis. Further, the numerical controller diminishes a set size which determines the time point to issue the first-mentioned sizing signal from the sizing device, toward a desired set size on a step-by-step basis with the increases in number of the workpiece ground after each truing.
U.S. Pat. No. 4,663,892 discloses a method of grinding a workpiece which is susceptible to deflection and/or deformation when grinding is carried out by relatively infeeding a grinding wheel to keep the wheel face and work surface in relative rubbing contact at an interface region, the method comprising continuously determining the force exerted by the wheel on the workpiece at the interface region as grinding conditions change, continuously applying to the workpiece at least one counterbalance force which in equivalent effect is opposite in sense to the determined force, and variably controlling the counterbalancing force to maintain its effective magnitude equal to the magnitude of the determined force.
U.S. Pat. No. 4,546,681 discloses a steady rest for alternatively supporting the internal and external surfaces of a tubular workpiece during a machining operation. Each outer end of a plurality of movable fingers includes first and second workpiece contact devices such as rollers. The second contact device is offset from the longitudinal axis of the finger so that it may engage the inner periphery of the workpiece. The opposite inner ends of the outer fingers ride in slots having opposing arcuate cam surfaces. One cam surface provides backup support for its finger when externally contacting the workpiece while the other cam surface insures stability when its finger is contacting the inner periphery of the workpiece.
U.S. Pat. No. 4,399,639 discloses a true centering steady rest for rotatably supporting an elongated cylindrical workpiece for a metal working operation on the outer diameter of the workpiece, such as a grinding operation. The steady rest includes a housing in which is slidably mounted a pusher arm carrying a workpiece center wear pad. A pair of side arms is slidably mounted on said pusher arm. Each side arm carries a replaceable wear pad engageable with a workpiece at a point in the range from 90xc2x0-140xc2x0 from the center wear pad. The center and side wear pads are moved into operative engagement with a workpiece when the pusher arm is moved toward the workpiece, and they are disengaged from the workpiece when the pusher arm is moved away from the workpiece.
U.S. Pat. No. 4,276,723 discloses a steady rest for supporting a workpiece to be ground comprising three contact shoes which are simultaneously movable toward and away from a workpiece centerline so that workpieces of varying diameter can be supported and maintained on a fixed centerline of rotation. The top contact shoe is mounted for pivotal movement to a position clear of the work area to facilitate loading and unloading of the workpiece. A hydraulic operator is provided for pivoting the upper contact shoe between the operative position, engaging a workpiece, and the loadunload position. A second hydraulic operator is provided which through appropriate mechanical wedges moves upper contact shoe and the two lower non-pivoting contact shoes simultaneously toward or away from a workpiece.
According to the present invention, there is provided a support for supporting a work piece to be machined. The support is for use in a machine adapted to receive fluid from a fluid source. The machine includes a tool for removing material from the work piece. The support includes a body defining a chamber therein and an inlet operably associated with the body. The inlet is in communication with the chamber. The inlet is adapted for communication with the fluid source. The support also includes an outlet operably associated with the body and in communication with the chamber. The outlet is adapted to provide a stream of fluid for supporting the work piece.
According to the present invention there is further provided a method for machining the cylindrical periphery of cylindrical work pieces. The method includes the steps of providing a machine for removing material from a work piece, placing the work piece in operating position within the machine, placing a support in a spaced apart relationship to the work piece, providing a fluid source in fluid communication with a fluid flow device, advancing the fluid within the fluid source with the fluid flow device toward the support, advancing the tool toward the work piece, flowing fluid from the support onto the work piece, machining material from the work piece with the tool, and providing a fluid force from the fluid flowing onto the work piece to oppose a tool force from the tool so that the deflection of the work piece by the tool is reduced.
According to the present invention there is further provided a roll made by the process of providing a machine for removing material from a work piece, placing the work piece in operating position within the machine, placing a support in a spaced apart relationship to the work piece, providing a fluid source in fluid communication with a fluid flow device, advancing the fluid within the fluid source with the fluid flow device toward the support, advancing the tool toward the work piece, flowing fluid from the support onto the work piece, machining material from the work piece with the tool, and providing a fluid force from the fluid flowing onto the work piece to oppose a tool force from the tool so that the deflection of the work piece by the tool is reduced.
According to the present invention there is further provided a grinding machine for use in grinding a work piece. The grinding machine includes a frame and a grinding wheel rotatably mounted to the body. The grinding machine further includes a motor for rotating the grinding wheel and an apparatus operably associated with the body for rotatably supporting the work piece in a spaced apart relationship with respect to the apparatus.